Apparatus for compacting newly poured concrete by directly coupled vibration

ABSTRACT

A method and an apparatus for compacting newly poured comparatively dry concrete or similar porous plastic raw materials (6) with a direct mechanically coupled 3-mass oscillatory system where the raw material in its confined form is vibrated and compacted from both sides by two vibrating planes with synchronized directional vibrations in phase opposition. Only one vibrating plane (M1) includes synchronized directional vibrators (4). Its other part (M3) is elastically coupled with (M1) by spacer means (8) (M2) arranged between a spring system (7) being so dimensioned that the parts is dynamically balanced whereby the two parts (M1) and (M3) oscillate in phase opposition close to or at the 2nd natural frequency of the system with a dynamic amplification of the amplitudes in relation to the impulses imparted from the vibrators (4) at the same time while (M2) is stationary. During the process (M1) and (M3) are carried towards each other by (M2) as the raw material is gradually compacted.

The invention relates to a method concerning compacting newly formedconcrete and the like by synchronized vibrations applied to oppositesides thereof, and to an apparatus for carrying out the method.

By conventional industrial production of concrete such as of largeconcrete units where the particles of the concrete are rearranged bygravitation and where it is the object of the vibration to reduce thesurface forces between the particles, there is often with a view to theworkability of the concrete added a large amount of cement and an amountof water that is 2-3 times larger than necessary for completelyhydrating the cement.

If the cement paste content is too big and moreover filled with poresdue to insufficient vibration and/or too big water content, a break inthe hardened concrete unit will extend in the cement paste coating theaggregate. This is due to the fact that the weakest component inconcrete is the cement paste. The strength of the aggregate is normally3-5 times greater than that of the cement paste.

Accordingly, it is important that the leanness of the concrete definedas the ratio of aggregate to cement (a/c) is as great as possible toobtain maximum material properties.

By intensively compacting lean and comparatively very dry concrete therate of strength development as well as final strength and the modulusof elasticity of the concrete are improved.

The rate of strength development depends on the degree of compacting sothat an increase in the specific weight of the concrete by 1% results ina reduction in hardening time by approx. 25%.

There is moreover obtained increased resistance to outer physical andchemical attacks, e.g. improved waterproofing and frost safeness.Concrete with a water/cement (w/c) ratio below 0.4 is considered frostsafe.

By intensive compaction the poor properties of the concrete are reducedwith a view to carbonization as well as creeping and contraction.

The problem of achieving such greatly improved properties has hithertobeen that by the low w/c ratios it has not been possible to rearrangethe particles of the concrete to reach sufficient compactness the resultbeing enclosed voids at a number and distribution acting as breakpromoters in the concrete.

During recent years producers have therefore added super-plastifiers tothe concrete mixes thus reducing friction between the individualconstituents of the concrete mix so that it is possible to work with awater/cement ratio of about 0.25 when simultaneously applying vibration.

These plastifiers are organic substances that are added to the concretemix and the long-term effects thereof are not known. Moreover, the useof plastifiers has the effect that the adhesion of the concrete to thereinforcement is reduced. It is therefore desirable to be able to avoidadditives of any kind so that there are only used mineral, i.e.inorganic, constituents in a concrete mix.

From German published specification DE No. 24 53 634 the technique ofwhich is today applied by all hitherto known concrete product machinesit is known to compact the enclosed mass of concrete by transmitting thevibration from an underlying vibrating table and through the concretemake a mass resting on the concrete oscillate. In this case the springaction of the piston in the cylinder is performed by having sameconnected with a hydraulic accumulator forming the spring unit. Byadjusting the pressure in the cylinder it is possible to make the upperpart oscillate when the squeeze pressure has been suitably balanced.

The arrangement is not a 2-mass system because the spring unit is notconnecting the two masses. On the contrary the two masses with springsystem belonging thereto each form a system with one mass and one degreeof freedom where by means of a static squeeze pressure the vibration istransmitted from the part containing the vibrator to the upper pistonvia the concrete.

The low efficiency of this oscillation system is due to the following:

(1) at the moment of impact the counter-oscillating part reduces theamplitude of the supplied impulses from the oscillating part containingthe vibrator,

(2) the oscillatory amplitude of the counterpart becomes dampened by theplastic impact with the deformable object,

(3) there is no rebounding force for the counterpart unless the staticsqueeze pressure is high (but then rearrangement of the concrete duringthe process is hindered),

(4) cylinder dampening due to friction between piston and cylinder walland to throttling loss in the oil,

(5) the reactions in the base give a great energy loss and noise to thesurroundings.

In order to achieve as described above that the amplitudes are phasedisplaced 180 degrees in relation to each other an outwardly excitedoscillatory system with one degree of freedom will have to work highlyovercritical (approx. 5-10 times) but then the amplitude of the upperpiston will approach zero and thus also the dynamic force. In this wayonly the generally known stamping is achieved where the vibrator strikesagainst a firm back-stop.

If as stated in German published specification DE No. 24 53 634 theoscillatory system was in resonance for achieving maximum amplitudes,the frequency would have to be kept within a range of +/- 5% but at thatpoint the phase angle is only offset 90 degrees and not 180 degrees asmentioned in the text and shown in the drawing. The vibrator mounted onthe upper piston is only used for releasing the finished object by thestripping.

From German published specification DE No. 25 52 852 it is known tocompact the enclosed concrete mass by transmitting the vibration from anunderlying vibrating table through the concrete and making a massresting on the concrete oscillate by making rebounds. There are noregular spring assemblies, i.e. the ballast plate merely rests on theconcrete surface thereby limiting the impact force of the ballast plateto the pull of gravity. It is also described that the plate can beconnected with cylinders which if being springy must then be adjusted tothe mass and the frequency as otherwise only the generally knownstamping is obtained. The upper part of the system with ballast pistonis like DE No. 24 53 634 an oscillation system which is excited fromoutside and through the concrete with the resulting low efficiency andparticularly because of the cylinder dampening there being no springsystem. The hydraulic cylinders mounted between machine frame and mouldframe are merely used for opening and closing the mould.

From German published specification DE 30 22 602 it is likewise known tocompact an enclosed concrete mass by two-sided vibration with asuperposed static pressure through the concrete. There vibration istransmitted to the upper piston which is simultaneously making slowhorizontal calendering movements during the process. The oscillatoryprinciple is as by the two above-mentioned an outwardly excitedoscillation system but here with particularly large damping of thetransmitted impulses between the pistons and the stationary cylindersbecause there are no kind of spring elements thereby reducing theamplitude of the upper part. As mentioned above the amplitude of thetransmitted impulses are further reduced by the counter-oscillatinglower part and by the plastic impact with the deformable object. Also inthis case the reactions of the cylinders against the base are lost withresulting energy loss.

By this oscillatory system where mould and unit are placed on thecounter-oscillatory lower part, the natural frequencies of the machineare changed dependent on the mass of mould and unit. It is thereforenecessary to change the working area of the machine individually inorder to obtain optimum compression but then the dynamic force issimultaneously changed.

The object of the invention is to provide a method and an apparatuswhereby it is possible to produce high quality concrete with a lowcontent of water and cement and with a (w/c) ratio reduced to a valueclose to the theoretical minimum of approx. 0.25-0.3 for obtainingcomplete hydrating.

According to the invention the two large masses exerting the dynamicforces on the plastic object are directly mechanically connected throughthe third mass for example the cylinders by means of spring elements andthus provide a true multiple mass system that can also be characterisedin that the oscillation may take place whether there is concrete in themould or not.

During the process the two large masses thus form each other's base inthat the impulse forces are equally large and opposite which was alsoestablished by measurements in that the cylinders connecting the twomasses stand still during the process.

This is achieved by proceeding as disclosed herein, for example byutilising an apparatus as disclosed. By intensively compacting concrete,however, it is not only the water/cement ratio which can be reduced butalso the absolute cement content per m³ concrete. The concrete mixcontains no plastifying additives whatsoever, i.e. it solely containsthe original inorganic constituents: water, cement, sand and stone.There is thereby obtained a highly uniform product having a more compactstructure than in the known products and thus a highly durable concretewith faster strength development and much higher ultimate strength.

The compacting machine is designed as a mechanically coupled oscillatorysystem and is made as a 3-mass system in such a manner that thecompacting masses oscillate in phase opposition. By the new process itis a matter of a highly intensive two-sided actuation of the plasticobject such as newly poured concrete, newly poured chipboard pulp,moulding sand and similar plastic masses where the enclosed object canbe acted on by huge dynamic forces.

Since the compacting machine is designed as a mechanically coupledoscillatory system, it will oscillate without an overlaid static contactpressure with the mould. It is thereby ensured that the rearrangement ofthe material is not hindered during the compacting process contrary tothe known concreting machines which must all transmit the impulsesthrough the concrete.

Contrary to the above identified known oscillation systems with onedegree of freedom where the amplitude of the counterpart is reduced bythe transmission of the vibrational forces through the plastic object,the invention provides enhanced oscillation of both parts compared withthe amplitude imparted by the vibrators since the oscillation of the twoparts are dynamically coupled and operate close to their 2nd naturalfrequency. This natural frequency is independent of the weight of mouldand unit because the dynamic actuation is of the same order on bothsides of the object and because the opposed accelerations of the planesare several times higher than acceleration due to gravity; i.e. theobject "drifts" between the two planes and thus the mass of the objectdoes not influence the 2nd natural frequency of the oscillatory system.

By proceeding as disclosed, for example by utilising an apparatus asdisclosed, it is ensured that the vibrational energy continues topenetrate into the newly poured concrete as the compacting proceeds andthe thickness of the unit is reduced.

The machine is designed as a 3-mass system wherein for example hydrauliccylinders with pistons or similar devices are used such as screw jointsthat gradually reduce the distance between the two planes as thecompacting process proceeds.

By this efficient vibrational system where the machine works close tothe 2nd natural frequency of the oscillatory system, the machineoperates as a mechanical dynamic amplifier of the transmitted impulses.The spring system is balanced in such a manner that there may beobtained an amplification of the dynamic forces corresponding to approx.10 times the vibrator force, such having been established by tests bymeasurements made with a two channel oscilloscope.

The two parts of the machine are made as highly rigid structures so thatno bending oscillations will occur within the working area which couldotherwise give rise to uneven compacting.

The spring system has been so balanced that the amplitudes of thecylinders are minimised in relation to the other masses and thus it isachieved that the opposite amplitudes of the two planes become as highas possible. Moreover, the amplitude of the pistons in the cylinders areminimised by applying a relatively high hydraulic pressure on both sidesof the piston. There is thus also achieved a high efficiency of thetransmitted vibrational energy in that the spring action is solelyperformed by the spring members arranged for that purpose and not inhydraulic cylinders where great damping would occur due to throttlingand friction.

By further proceeding as disclosed, it is not necessary to overlay theoscillation with a static pressure in order to maintain the oscillationof the part not containing the vibrator arrangement and it is thusensured that the rearrangement of the material is not hindered duringthe compacting process.

Finally, the apparatus according to the invention can be designed suchthat the same hydraulic cylinders with pistons can be used for the meanswhereby the two parts are gradually carried to each other during thecompacting process as well as for the means whereby the apparatus isopened when the compacting is concluded.

The invention will be further described in the following with referenceto the drawing wherein:

FIG. 1A shows a schematic drawing of a prior art 2-mass oscillatorysystem.

FIG. 1B shows a graph of the oscillation course of a system such as thatshown in FIG. 1A.

FIG. 2A shows a schematic drawing of a 3-mass oscillatory systemaccording to the instant invention.

FIG. 2B shows the oscillation course of a system such as that shown inFIG. 2A.

FIG. 3 shows conventional concrete vibration where the vibration is notdirectional,

FIG. 4 shows the principle of the invention with synchroniseddirectional and evenly distributed vibrations imparted to one part (herethe lower part) in the compacting machine,

FIG. 5 shows the apparatus according to the invention in greater detail,

FIG. 6 shows to the left a concrete mix that can be used according tothe invention and to the right a concrete mix that can be used by theknown machines, and

FIG. 7 shows the strength development as a function of time partly byusing the invention and partly by using conventional techniques.

FIG. 1A of the drawing shows a 2-mass oscillatory system having massesM1 and M2. If synchronised directional vibrators are arranged in one ofthe parts for example the lower part M1 having the force Fsin (ωt), themasses will oscillate from their positions of rest which is symbolicallyshown in FIG. 1A by the oscillatory amplitudes X1 and X2 in accordancewith generally known oscillation theory. In FIG. 1B of the drawing theoscillatory course is graphically shown as a function of frequency theoscillatory amplitude being shown in relation to the static amplitude.

In FIG. 2A of the drawing there is shown a 3-mass oscillatory systemhaving masses M1, M2 and M3.

By way of example mass M1 can be the lower part of the machine, mass M2is the hydraulic cylinders with pistons and mass M3 is the upper part ofthe machine. The masses are flexibly mounted over each other and rest ona base by means of the spring members each having spring rigidity K1, K2and K3 and dampings C1, C2 and C3.

If synchronised directional vibrators are arranged in one of the parts,for example in the lower part M1 with the force (ω²) sin (ωt), the threemasses will oscillate from their positions of rest which aresymbolically shown in FIG. 2A by the oscillatory amplitudes X1, X2 andX3.

By means of a computer program it is possible to optimise the springmembers giving the desired oscillation picture, namely a form ofoscillation where upper and lower part oscillate in phase opposition sothat the desired impact forces are achieved while the spring forces arekept below a certain level. FIG. 2B shows the oscillation course ofupper part X3 and lower part X1 by a picture of the oscillatoryamplitudes as a function of the frequency of the vibrators. There areused synchronised rotating oscillation mass vibrators.

It will appear from FIG. 2B that it is both theoretically andtechnically possible to have upper and lower parts oscillate in phaseopposition over a reasonable range, for example in the range of 60-80Hz.

FIG. 3 of the drawing shows the operation of conventional concrete unitvibrating where a lower part 1 with spring members 2 are placed on abase 3. Vibrators 4 are arranged in the lower part. On top of the lowerpart there is placed a mould table 5 with a newly poured concrete unit6. Usually the vibrators 4 are not synchronised and the resultingvibration is therefore not directional.

By the present invention conventional concrete vibration is improved bymeans of the apparatus shown in FIG. 4.

The apparatus in FIG. 4 forms a 3-mass oscillatory system correspondingto FIG. 2A. The spring members, spring system, situated between upperand lower parts comprise springs 7 and spacer means such as hydrauliccylinders with pistons 8. On either side of pistons 8 there are appliedvery high hydraulic pressures of the order of 300 Bar so that alloscillation will take place in springs 7. By changing the hydraulicpressures upper part and lower part can be carried towards each otherduring the vibrating as the rearrangement proceeds.

The vibrational energy is transmitted from lower part to upper partthrough the flexible units consisting of springs 7 and hydraulic pistons8 so that the two parts oscillate in phase opposition and close to thesecond natural frequency, cf. FIG. 2B.

FIG. 5 shows in greater detail how the method and the apparatusaccording to the invention are carried out and used in practice. Thenewly poured concrete unit 6 having first and second opposite surfacesis shown prior to the compacting, the fat black stroke 9 showing theexcess that is pressed down by the compacting/vibration. By way ofexample such a machine can compact a storey-high concrete panel or aconcrete slab unit in approx. 1 minute by a frequency of between 50 and80 Hz on the synchronised vibrators. In case of smaller objects and acorrespondingly smaller machine such as a concrete product machine, aslab of 100 kg (1/2 m²) for example can be compacted in 5-15 seconds bythe mentioned frequency area.

Tests have shown that apart from savings in cement, the higher finalstrength, the faster strength development and the high resistanceagainst of the concrete to physical and chemical action there are alsoachieved other great advantages in relation to the known machines.Firstly, the noise level is substantially reduced so as to lie severaldecibel below the level of the known machines. Secondly, oscillations at2nd natural frequency causes the oscillation energy to remain in thesystm so that it is not necessary to place the machine securely anchoredin a big and heavy base which is always the case by the known machines.

The machine according to the invention is thus fairly mobile. Finally,the energy consumption have proved to be far less than by the knownmachines because the machine according to the invention gives a two-sideamplification of several times the dynamic forces.

FIG. 6 of the drawing shows to the left a concrete mix which can be usedby the method and the apparatus according to the invention, and to theright a concrete mix which is used by the known machines. By theinvention it is possible to reduce the water/cement ratio and it is alsopossible to reduce the absolute content of water and cement so that thepore volume (p) is reduced. There is thus obtained a stronger type ofconcrete, faster strength development and shorter stripping time. Theconcrete mix contains no plastifying additives of any kind.

FIG. 7 of the drawing shows the strength development as a function oftime partly when using the invention, cure I, and partly when usingknown techniques, curve II. Both concrete mixes are made with the sameMiddle East Portland cement at an amount of 300 kg cement per m³concrete mix.

Test results

A. The basis of the development of the invention has been tests made inthe Middle East by the production of hollowcore units with short curingtimes by using Middle East Portland cement.

By the tests units were stripped at w/c=0.3 and 300 kg cement/m³ after 2hours' steam curing. After 15 maturity hours (M20), (equivalent curingtime at 20° C.) the compressive strength were measured at 20 MPa.

In comparison it should be mentioned that the units obtained byconventional production with the same cement content must have 5 hours'steam curing to achieve the stripping strength 10 MPa., see FIG. 7.

The test results of full scale tests are marked on FIG. 7 of thedrawing, curve I.

B. A concrete product machine is built up as shown in FIG. 4 of thedrawing but mounted in a framework for mutually centering upper part andlower part. The two parts facing the concrete are ground plane and eachhave an area of approx. 1 m². By tests with this machine it wasestablished by measurements made with a two channel oscilloscope and bythe use of the stroboscope light that the two parts of the machineoscillate completely as assumed, i.e. the two large masses (upper partand lower part) oscillate in phase opposition and the hydrauliccylinders stand still when a poured concrete unit is compacted.

We claim:
 1. An apparatus for compacting newly poured porous rawmaterial such as concrete by directly coupled vibration compacting; saidapparatus including two vibrating planes adapted to enclose a unit ofporous raw material to be compacted; said apparatus including meanswhereby only one of the vibrating planes includes synchronizeddirectional vibrators; and, said apparatus being further characterizedin that a second plane is coupled with a first plane by means includinga spring system dimensioned and tuned so that the two planes may beoscillated in phase opposition at about a 2nd natural frequency of thesystem with a corresponding dynamic amplification of the amplitudes ofplane vibration in relation to impulses imparted from the vibrators;said spring system including spring parts arranged at opposite sides ofspacer means operable to gradually reduce a distance between the twoplanes as compacting of newly poured porous material proceeds.
 2. Anapparatus according to claim 1 further characterized in that the spacermeans is adapted to selectively carry the two planes away from eachother when a compacting is concluded.
 3. An apparatus for compacting aunit of newly poured porous material, such as concrete, having first andsecond opposite surfaces; said apparatus comprising:(a) a first vibratorplane operatively positioned to transmit compacting vibration to thefirst surface of the unit of newly poured material; (b) a secondvibrator plane operatively positioned to transmit compacting vibrationto the second surface of the unit of newly poured material; (c) a spacermeans positioned between said first and second vibrator planes; saidspacer means including first and second spring oscillation means;(i)said first spring oscillation means engaging said spacer means with saidfirst vibrator plane; (ii) said second spring oscillation means engagingsaid spacer means with said second vibrator plane; and (iii) said spacermeans and first and second vibrator planes forming an oscillationsystem; and, (d) vibration means for vibrating said first and secondvibration planes in phase opposition at about a 2nd natural frequency ofsaid oscillation system; (e) whereby a unit of newly poured porousmaterial operationally positioned between said first and second vibratorplanes may be compacted.
 4. An apparatus according to claim 3,wherein:(a) said spacer means includes means to selectivelyoperationally reduce a distance between said first and second vibratorplanes to accomodate for compaction of a unit of newly poured materialoperationally positioned therebetween.
 5. An apparatus according toclaim 3, wherein:(a) said spacer means includes a plurality of hydraulicpistons and cylinder assemblies oriented for selectively moving saidfirst and second vibration planes apart from one another followingoperation to compact said unit of newly poured porous material.
 6. Anapparatus according to claim 3, wherein:(a) said vibration meanscomprises a plurality of vibrators in direct engagement with said firstvibration plane; and (b) said second vibration plane is without avibrator in direct engagement therewith and selectively vibratessubstantially only in response to motion generated by said vibrators indirect engagement with said first vibration plane.